Acid treatment of heterocyclic imide and imidazole vat dyestuffs



Patented June 14, 1949 ITED STATES ATENT OFFICE ACID TREATMENT OF HETEROCYCLIC IMIDE AND IMIDAZOLE VAT DYESTUFFS Maine N Drawing. Application March 13, 1944, Serial No. 526,341

7 Claims. 1

This invention relates to an improved process of transforming vat colors into a form having a ver fine and substantially uniform particle size.

More particularly, the present invention relates to an improved process whereby dyestuffs in the desired uniform, finely-divided state are obtained from vat dyestuffs derived from cyclic imides of polycarboxylic acids, including those wherein the heterocyclic imide is fused to give an imidazole nucleus. The most valuable dyestuffs of this group are derived from naphthalene l,4,5,8-tetracarboxylic acid and from perylene 3,4,9,10-tetracarboxylic acid. The following are typical examples of such dyestuffs:

I O O Perylene 3,4,9,10-tetracarboxylic acid bis-methylimide ment in concentrated sulfuric acid and reprecipitating it by dilution with water, usually by drowning the entire solution in a large excess of water. Modifications have been proposed in 5 which the dilution is carried out in other ways.

These have included, for example, addition of dilute sulfuric acid in a quantit only sufiicient to precipitate a sulfate which can be collected and hydrolysed; or accomplishing the dilution with water of crystallization by using such hydrated materials as Glaubers salt and the like. The effect of varying the operating temperatures has also been proposed as a means of control.

While the art has succeeded in obtaining finer particle sizes, the importance of uniformity and its necessary relation to fineness was not properly considered. In general, therefore, vat colors as prepared according to the teachings of the prior art generally lacked sufficient uniformity of particle size and contained larger particles in addition to the small ones. As a result, there remained a demand for a method adapted to produce a more finely divided color of more uniform size.

It is, therefore, a principal object of the present invention to develop such a process, capable of producing particles having the desirable properties of fineness and uniformity of particle size. In general, the desired object is accomplished through an improved process of carrying out the treatment of the materials with sulfuric acid.

According to the present invention, it has been found that in the treatment with sulfuric acid, there is for each material a specific range of acid concentrations which produce the optimum result. In addition, it has been found that the proportions between the dissolved and undissolved Perylene -3,4,9,10-tetracarboxylic acid bis-p-anisidide As is well known, vat colors are normally obtained as coarse crystalline materials or as relatively large agglomerated particles. In this condition, they are unsuitable for use in printing, pigment dyeing, emulsion printing and the like operations. As a consequence, various procedures have been proposed to reduce their particlesize and thereby improve their penetrating ability and reactivity.

Commercially, the most common of these procmaterial at any stage in the process is of equal, if not greater importance. This involves not only the acid concentration, but also the total amount of acid present. Variations also result from changing the temperature at which the reaction is carried out, the procedure by which the correct acid concentration is reached and to a lesser extent with the time of contact. All must be reasonably controlled for the best results.

In developing the present process, the optimum esses comprises the steps of dissolving the pigacid concentration and amounts used are h i 3 that only a very small quantity of dyestufl' is dissolved at any one instant. The dissolved dye becomes converted to and precipitated as its sulfate. It is necessary that ,thedyestuil have some solubility, otherwise it cannot be converted into a sul- 5 fate, and it is further necessary that at least one of its sulfates be slightly less soluble. It is the recognition and use of this difierential solubility between the dyestufi and itssuliatewh chis. responsible for the surprisingly improvedifsult'sobe tained by the process. The dyestufflpeing slightly soluble, goes into a solution limited "tent as such and is quickly converte, it s siillate. But because the salt is less soluble than the dye, the solution becomes supersaturated with re ct to the sulfate and part of the latter soosrat; and more dye is dissolved. Thus the conversion is progressively carried out until substantially complete. It should be noted that atany given time. the solution or the sulfate excee "any snore, Coil; sequently, the dissolved molecules are relatively far apart and their rate of, fegation in. pro: cipitati n g the insoluble s llfatesfis lfl'ery low. At the same time, because the concentration of sulf ate remains essentially, onstant during the en; tire precipitation, the pre pitated prodiicts, are not only very. finely divided but have avery uniform size. Probably due to a ,pseudomorphosis, this fineness and uniformity is r etained when they are subsequently hydrolysed with water, either with or without being previouslyisolated. l i x s in. n r classmates h r c s of h p t n e el qom r e' he t e ment of vat dyestuffs characterized by the pres ence of cyclic imidesof polyc w eluding those wherein the heterocycl c i fused to g e da qlenuc ella ih 1% root amount of sulfuric acid having the op H m concentration. At the same ti thepro er dee of c r is ex rcised 11. .1 7 .Ji eel? h correct o centrat n e ar us rea an: taining a substantially uniform temperature throughout h QQ5$.-..;...

Acco d n ot e o e Onei a cipal factorsto be contro e c'l arez ,(1 the g, concentration; (2) theamountof acidiiii}, the temperature; and (4). the rnann r.of reaching,tl e ac d o e n rai qn-.lfie .ef il direct bearing on the. treatment, of any part M dyestufi, Consequently, each factor is subject to certain limitations.

. .As fa a t idfio e the individualdyestuffs vary widely, their timum. acid ranges. For partic ar dyestufi the exact ac r e. mo .suitable.i iete sme i not be assigned numerical limitations which will in turn be applicable to all cases. Functionally, a more exact limitation can be assignedin terms or solubility. The lower limit is that acidbohilegtla; tion at which the specific dyestufl has a slight solubility. The upper limit is that concentration at which a sulfate of the dyestufi has only a very limited solubility, so as to form readily a supersaturated solution or the sulfate.

Intreating the polycarboxylic acid imide and im'adazole vat dyestuffs of the present invention; it is important that the sulfuricacid be diluted to the proper concentration before being used. If the dyestuff is first dissolvedin concentrated acid and the resultant solution istheii diliited to the proper strength, the desirable result is not obtained. In some cases 'thedyestiifi' itself is 'attacked by the cofic'ehtrated'acid. In other oases only a coarse material is obtained probably beabaoiis cause precipitation by diluting a rather concen-' trated solution favors the formation of large particles. It is desirable, therefore, to have the initial concentration as low as is practically possible; 5 I P So far as the amount of acid used is concerned, at least of the solid products present, i.e., the dyestuff as such or in the form of its sulfate, should remain undissolved at any point in the process. Preferably, the undissolved material should be as greatas practically possible so that 9' or more, remains undissolved. Because the ofundissol'ved material present during the process is an important consideration, there is obviously an interrelation between the acid concentration and the amount of acid used. The latter, however, is not as critical as the former. As pointed out above, the amount of acid used may vary. To a certain extent this is limited by practical considerations. Obviously, an insufficient amount of acid produces avery thick, unstirrable slurry. On the other hand, too ore-a o amount of acid is impractical because of the volume requiredand the consequent decrease in the productive capacity of the equipment. At the same time, too great an amoontor acid will dis solve excessive amounts oithedyestufi and s E fate. As was indicated above, thisis undesira e if theoptinium fineness and uniformity of parti'-' cles size is to be obtained. I

For all practical purposes, the amount of acid used will be found to be about 10 to 40 part "or part of dyestuff. However in all but extreme cases, these limits can b'considerably narrowed.

solubility of materialsin any designated,strength of acid. Therefore thejeinperature of the reaction should not beallowed tQ.,,Ya y sufficiently to appreciably aiTe'ct the solubility during the course of the reaction. It is most convenient to work at i la elrr a te perature -ilenseq m the experimental use. taken in developing the present invention i s basedv on temperatures of about 25-35 C However, should; it become desirable to operate at higher or lower temperaatures, an adjustment in either; or both the strength and amount'of acid tocompens'ate theremsan er adi y.macletiaac qrq n with the solubility limitationsset forth above.

The time cycle sl'iould'also be considered. Ob-

- viously i i ti'ie time of contact is too short al l of the pigment will not be converted into finelydivided'. sulfate. On the other hand, if the time. oiotania t s...,lln l l emise particles A good general practice is to drown the slurry in about 4 to 8 times its volume of water. .The precipitated product may then be isolated after diluting the solution to a convenient acid strength for practical-filtration.v Subsequently, the dyestuff is usually Washed on the filter until neutral. Preferably, but not necessarily, this washed filter cake is subjected to further treatment with a suitable deflocculating agent.

As an indication of the efficiency of the process, the following test has been found particularly useful. About 100-200 mg. of dispersed dyestuif is suspended in 200 ml. of distilled water at about 50 C. and approximately one-half of this suspension is poured on a three inch conical, glass filter funnel fitted with a dry N0. 1 Whatman filter paper. The suspension is allowed to filter by gravity. If the dyestuff is finely divided and uniformly dispersed, most of it should go through the filter into the filtrate, and the residue on the paper should be small.

Test dyeings are then carried out, using the filtrate and the unfiltered portion of the suspension, the strengths of the resultant dyeings being compared. The filtrate of a well-dispersed product gives a dyeing having about 75-90% the strength of the unfiltered product. It is readily apparent that the greatest dye strength from the filtrate is obtained only when the procedure of the present invention has been carried out so as to produce a maximum of finely divided particles of uniform size.

It is surprising, and entirely unexpected, in view of the prior art teaching that the use of more concentrated acids than are indicated by the limits of the present process produces a great amount of coarser particles as shown by the filtration test. Probably it is due to the fact that the strengths of acids usually prescribed by the prior art have too great a solvent action on the dyestuff. As a result, the solute molecules are closer together and have a greater chance to precipitate as larger particles of the sulfate. Obviously also, still more concentrated acid will dissolve substantially all the dyestufi", so that the sulfate will be precipitated only after dilution. This is the customary old acid pasting method and subject to all the ordinary faults which have been noted above.

Thus the principal advantage of the present invention lies in its ability to produce very small particles of uniformity of small particle size is of great importance, for example, in a pigment padding process. In such a process, fineness is essential to good penetration but if the particle size is not uniformly small, the coarser particles do not penetrate to the same extent as the finer material and uneven dyeings result. Similarly, in printing vat dyestuffs a fine product size is important in order that reduction may take place quickly, but if uniformity is lacking the resultant print is not properly level.

The invention will be more fully illustrated in connection with the following example in which all parts are by weight unless otherwise noted.

Ercample One part by weight of the dyestuff of Formula Number III was treated with 25 parts by weight sulfuric acid of various strengths for 23 hours. An 81.3% acid did not produce a uniform prodnot of the desired fine particle size; the filtrate obtained from the filter test above gave only 60% dyeing strength when compared with the unfiltered material. However, an acid of the 6. strength 85.2% gave a very uniform, finely dispersed material; the filtration test showed that the filtrate gave 90% dyeing strength when compared with the unfiltered product. Raising. the acid to a concentration of 88.9% gave a slightly inferior product, the test filtrate showing only dyeing strength when compared with the unfiltered product. At higher concentrations the resultswere still less favorable. The sulfate of the dyestuff precipitates in the form of bluishmaroon crystals. By way of comparison when the dyestufi was first dissolved in concentrated sulfuric acid, diluted with water to give a slurry of one part of dyestuff with 25 parts of sulfuric acid of 85% concentration, and stirred for 18 hours, the resulting material was not as finely dispersed. The filtration test showed that the filtrate gave only 60% dyeing strength when compared with the unfiltered product.

We claim:

1. The method of converting a vat dyestuff of the group consisting of naphthoylene (184,5)- bis-imidazoles and perylene-3,4,9,10-tetracarboxylic acid diimides into very finely divided particles of substantially uniform size which comprises forming a slurry of the dyestuff with about 2040 parts of sulfuric acid per part of dyestuff, said acid .being used in such concentration and amount that at the reaction temperature at least a part, but not more than 10%, of the total dyestuff is in solution at any one time, agitating this slurry until conversion of the dyestuif to the substantially insoluble sulfate is substantially complete, and hydrolyzing the sulfate to the dyestufi.

2. A method according to claim 1 in which the amount and concentration of acid used is so balanced that not more than two percent of the dyestuff is dissolved at any time during the operation.

3. The method of converting a vat dyestuff comprising perylene-(3,4,9,10) -tetracarboxylic acid bis-methylimide into very finely divided particles of substantially uniform size which comprises forming a slurry of the dyestuff with about 20-30 parts of sulfuric acid per part of dyestulf, said acid being used in such concentration and amount that at the reaction temperature at least a part, but not more than 10%, of the total dyestuff is in solution at any one time, agitating this slurry until conversion of the dyestuff to the substantially insoluble sulfate is substantially complete, and hydrolyzing the sulfate to the dyestufi'.

4. A method according to claim 3 in which the amount and concentration of acid used is so balanced that not more than two percent of the dyestuif is dissolved at any time during the operation.

5. A method according to claim 3 in which the concentration of acid used is from about 83-90%.

6. The method of converting a vat dyestuif comprising perylene-3,4,9,10-tetracarboxylic acid bis-p-anisidide into very finely divided particles of substantially uniform-size which comprises forming a slurry of the dyestuff with about 20-30 parts of sulfuric acid per part of dyestuif, said acid being used in such concentration and amount that at the reaction temperature at least a part, but not more than 10%, of the total dyestuff is in solution at any one time agitating this slurry until conversion of the dyestuif to the substantially insoluble sulfate is substantially complete, and hydrolyzing the sulfate to the dyestuff.

7. A method according to claim 6 in which the REFERENCES CITED:

he following e ere ws r of mcqrdm file of this patent:

UN D STAT P TI TS.

Name Date Steindorfi; et a Jug-13, 1915 Number Name; bate; Eckert; June 24;,1930 Eckertr. vmm. 22; 1932 Eckent Nov. 22;1932 Nawiasky et a1. Oct; 10-, 19.33 Waldnon: Dec. 29 19.36 Hewett: Sept.'.27;. 193.8 Cant: ,.Apr.1,. 194:2 Detrick June 2, 19.42 FQREIGNMW:

Countr Gneat==i3ritain ,5.- L931 

